1. Field of the Invention
The present invention relates to an electron gun for a color cathode ray tube, and more particularly, to a dynamic focus electron gun for a color cathode ray tube having improved electron beam passing holes aligned in-line and forming a quadrupole lens.
2. Description of the Related Art
In general, an electron gun for a color cathode ray tube (CRT) is installed at a neck portion of a CRT for emitting electron beam. The performance of a CRT is determined by a state in which an electron beam emitted from the electron gun lands on a fluorescent film. Thus, many electron guns have been developer which can improve a focus feature and reduce aberration of an electron lens so that the electron beam emitted from the electron gun accurately lands on a fluorescent point of the fluorescent film.
As an example of the electron gun, electron beam passing holes of a vertical slot type and electron beam passing holes in a horizontal slot type for forming a quadrupole lens at an exhaust surface of a focus electrode and an incident surface thereof facing each other, respectively. A blade inserted into the electron beam passing holes formed at the exhaust surface of the focus lens disposed at a cathode""s side, is formed at the upper and lower sides of the electron beam passing holes formed at the incident surface of the focus lens.
In the electron gun for a color CRT having the above structure, in forming the quadrupole lens, as a vertical focusing force becomes weak by the electron beam passing holes in a horizontal slot type formed at the exhaust surface of the focus electrode, a dynamic voltage needs to be applied to an electrode. Also, in forming another quadrupole lens, as the blade is formed at the upper and lower sides of the electron beam passing holes of the electrode, the manufacture of electrodes is difficult and distribution between electrodes is not regular.
Another example of the conventional electron gun for a CRT is disclosed in U.S. Pat. No. 5,036,285. The electron gun includes first and third electrodes having holes, through which electron beams pass, formed in a keyhole shape in a horizontal direction for each of the beams, and a second electrode interposed between the first and third electrodes and having holes formed in a keyhole shape in a vertical direction for each of the electron beams. A dynamic focus voltage is applied to the first and third electrodes and a constant voltage is applied to the second electrode.
In the electron gun for a color CRT having the above-mentioned structure, an electron lens is formed between the first, second and third electrodes as the dynamic focus voltage and the constant voltage are applied to the first and third electrodes and the second electrode, respectively, so that a focus feature and a convergence feature are improved and the profile of an electron beam is corrected. However, the above electron gun exhibits high sensitivity because the quadrupole lens is too intensive and the adjustment of a voltage is difficult because the shape of a beam varies too much. Also, each of the electron beam passing holes formed in the electrodes forming a quadrupole is not circular and, as the electron beam passing holes overlap many times, distortion of the electron beam which is not preferred prevails and assembly thereof is not easy. Accordingly, the degree of alignment according to the assembly of electrode deteriorates.
To solve the above problems, it is an objective of the present invention to provide an electron gun for a color CRT which can reduce the distortion of the profile of an electron beam passing an electron lens by adopting as few circular passing holes as possible, and improving a focus feature by forming a quadrupole lens having an appropriate lens multiplier.
Accordingly, to achieve the above objective, there is provided an electron gun for a color cathode ray tube which comprises a first electrode to which a waveform alternating voltage or a static voltage is applied and where three vertical slot type electron beam passing holes are formed, a second electrode installed at one side of the first electrode, where circular electron beam passing holes are formed, and a third electrode disposed at the other side of the first electrode, where a single horizontal slot type electron beam passing hole is formed and to which the same dynamic focus voltage as that in the second electrode is applied.
According to another aspect of the present invention, there is provided an electron gun for a color cathode ray tube which comprises a first electrode to which a waveform alternating voltage or a static voltage is applied and where three circular electron beam passing holes are formed, a second electrode installed at one side of the first electrode, where horizontal slot type electron beam passing holes are formed, and a third electrode disposed at the other side of the first electrode, where circular type electron beam passing holes are formed and to which the same dynamic focus voltage as that in the second electrode is applied.
According to yet another aspect of the present invention, there is provided an electron gun for a color cathode ray tube which comprises a first electrode to which a waveform alternating voltage or a static voltage is applied and where three vertical slot type electron beam passing holes are formed, a second electrode installed at one side of the first electrode, where horizontal slot type electron beam passing holes are formed, and a third electrode disposed at the other side of the first electrode, where circular electron beam passing holes are formed and to which the same dynamic focus voltage as that in the second electrode is applied.